Fast forward 13 years to yesterday, when the folks at the Gorilla Foundation heard about Robin’s passing. According to Dr. Penny Patterson, who acts as Koko’s mentor and surrogate mother, Koka overheard a phone conversation about Robin’s death.

About a half-hour later, Patterson told US Weekly, Koko signed “Cry Lip,” and “became very somber, with her head bowed and her lip quivering.”

The theory here is that Koko remembered Robin, and like so many others, mourned his death.